Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Optical fiber lasers and amplifiers are used to radiate light at specific wavelengths, typically at relatively high intensities. Lasers and amplifiers generally include one or more amplifier stages, each including a length of active optical fiber typically coupled to one or more pump radiation sources (e.g., pump lasers) and configured to amplify optical radiation passing through a core.
The output power of optical fiber lasers and amplifiers is being continuously scaled up by designers. However, attempting to scale the output power can introduce problems, such as adverse energy dissipation effects. One intrinsic loss due to the pumping process results from the so-called quantum defect. The quantum defect is defined as the ratio of the pump wavelength to the lasing wavelength, and as such, acts as a measure of the amount of pump energy that is not carried by the amplified radiation, and thus is converted to excess energy within the fiber. Such energy can result in negative thermal effects or negative radiation effects (e.g., spontaneously emitted photons escaping from the fiber and not contributing to amplification of the electromagnetic radiation in the core). This can be particularly problematic in active optical fibers doped with elements having high quantum defect values. Another loss mechanism results from the emission of phonons (i.e., lattice vibrations). Such phonons can lead to an increase in thermal energy of the amplifier. In severe cases, the fiber itself can experience degradation due to overwhelming heating because of the associated energy dissipation effects. This is particularly the case for high peak power fiber amplifiers where the active doped fibers absorb the pump energy over a relatively short distance in order to mitigate substantial adverse non-linear optical effects (e.g., stimulated Brillouin scattering or stimulated Raman scattering).
Since a substantial fraction of the gain in an optical fiber amplifying system usually takes place within the portion of the active optical fiber that is nearest to the pump optical source (e.g., within a few centimeters of the end of the fiber coupled to the pump source), the thermal effects can be most pronounced in this region. This can be particularly problematic near fusion splices, sometimes called “critical junctions”. Thus, the fusion splices can be the first section of an optical fiber amplifying system to fail if the thermal effects are not adequately accounted for.
Therefore, in order for optical fiber amplifiers and lasers to maximize power output, an effective means of handling the adverse energy dissipation effects in such systems without adversely affecting other aspects of the system, can be desired.